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REVIEW PAPER

Fatigue behavior of cortical bone: a review Jingwen Li1 · He Gong1 Received: 3 August 2020 / Revised: 1 September 2020 / Accepted: 28 September 2020 © The Chinese Society of Theoretical and Applied Mechanics and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Fatigue is a common cause of bone failure. As the main load-bearing tissue, cortical bone carries a considerable share of load in the whole bone. Under cyclic loading condition, microdamage may generates and accumulates in cortical bone, which further triggers the fracture of bone. It is crucial to explore the fatigue properties of cortical bone and the influential factors for both clinical diagnosis and establishment of models that can predict fatigue failure of human cortical bone. In this review, the fatigue behavior of cortical bone was investigated. Through the complex hierarchical structure and self-repairing process, the risk of catastrophic fracture is reduced. Based on these understandings, the multiple influential factors of cortical bone fatigue properties were analyzed, which were considered to be a combination of internal and external factors. The internal factors include material properties of bone composition (i.e., mineral, organic material, and water) and bone structure. External factors refer to loading condition such as frequency, amplitude and direction of load. Besides, age, disease, radiation exposure and other factors affect the fatigue behavior of bone by altering one or more factors mentioned above. Keywords Cortical bone · Fatigue · Microdamage · Influential factor

1 Introduction Bone is the major load-bearing tissue of human body. When loading exceeds its resistance, a catastrophic failure takes place. Fatigue is a common cause of bone failure. With microdamage generation and accumulation, mechanical properties of bone deteriorate under continuous cyclic loading, and finally fracture occurs below its theoretical static yield strength. This failure is referred to as “stress fracture” in clinics. Stress fracture can be divided into two cohorts, i.e., fatigue fracture and insufficiency fracture. The former is very common in normal bone, especially in young population who experience strenuous exercise, such as athletes and soldiers. Their bones tend to be exposed to abnormal/repetitive cyclic loading condition. The latter, on the contrary, is often diagnosed in abnormal bone tissues with changes in structure or material properties. The patients are older and cannot bear physiological load [1, 2]. For engineer-

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He Gong [email protected] Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing 100191, China

ing material, its structure needs to resist the maximum static load, but more importantly, to sustain a certain number of loading cycles. Similarly, bone tissue bears a large amount of cyclic load under physiological conditions,